This invention relates to the field of airport runway marker lamps and comprises an improved structure which provides a breakaway lamp post which is capable of separation from its base without permanent damage to the post and which consequently may be easily and rapidly re-erected by maintenance personnel.
Maintenance requirements of runway marker lamps are a continuous source of work for airport personnel. Due to the importance of reliable lighting in nightime aircraft landing and movement, these lamps should be operating at all times and down time must be minimized.
Traditionally, such lamps have been mounted on upright metal posts which have a threaded lower end which screws directly into a ground-mounted electrical junction box. The metal posts are deeply scored adjacent the threaded lower end so that, if the post is struck by an aircraft or other vehicle, the post will break or snap along the scoring. Such breakaway feature is recognized as an important safety requirement, and the described construction has been standard equipment at airstrips for many years.
While the scored metal posts are reliable and long lasting, they are quite difficult to replace when breakaway occurs during collision, and marker lamps are struck and broken with considerable frequency. Breakage is particularly likely during inclement weather, as for example when aircraft may be landing on slippery runways or under lateral wind conditions, causing sideward movement of the aircraft and resulting collision between the lamp and the aircraft body. Under such conditions, one or more lamps may be snapped off during landing. In the northern climates where snow accumulation is a constant problem during winter seasons, snowplows also strike and break the runway lamps. With the presently used scored metal posts, breakage of a post results in the lower threaded end of the post being lodged within the electrical junction box and requires that the lower end of the post be chiseled out. Such removal requires a workman to laboriously chip the broken threaded end from the socket using a cold chisel and can be a tedious, time-consuming operation, particularly when the broken end may be rusted or corroded within the threads of the electrical junction box. Such repair is still more onerous when done in sub-zero temperatures and frigid wind chill conditions on the open runway.
Still another problem which can arise during breakaway with the now used, scored metal post is that the fairly sharp fractured rim of the post which remains along the scoring after breakaway is sharp and jagged enough to strip or cut the electrical wiring passing from the electrical junction box upward through the post and, accordingly, wiring damage may also occur during breakaway and can require further time and effort for repair.
Another shortcoming of the presently used marker lamps is that they are a fixed height and cannot be varied. In many parts of the world where snowfalls accumulate, it is desirable that posts be able to be raised so as to be visable over the snow. However, posts placed so high as to extend over snow accumulations are too high to easily accommodate grass mowing equipment during the summer months. It would be desirable to be able to raise the post level during the snowy months and to easily lower the level during the summer so that sickle bar mowers may work the grassy areas and still be able to elevate their sickle bars to pass over the posts. The problem is solved by the present invention.
Accordingly, with the problems of maintaining the known airport marker lamp systems, it is desirable to provide an improved breakaway marker lamp which is reuseable, reliable, resistant to breakage, and rapidly and inexpensively repaired. The present invention accomplishes these objectives.